Associative Database Scanning and Information Retrieval

ABSTRACT

A method and device are disclosed for an associative and approximate, analog or digital scanning of databases that allows for the asynchronous accessing of data from a mass storage medium. The invention includes providing dedicated analog and digital circuitry and decision logic at the mass storage medium level for determining a key identifying the data of interest, continuously comparing the key to a signal generated from a reading of the data from the mass storage medium with an approximate or exact matching circuit to determine a pattern match, determining a correlation value between the key and the data as it is read in a continuous fashion, and determining a match based upon a preselected threshold value for the correlation value. The pattern matching technique eliminates any need to compare data based on its intrinsic structure or value, and instead is based on an analog or digital pattern. The key and data may be either analog or digital. This device and method may be provided as part of a stand-alone computer system, embodied in a network attached storage device, or can otherwise be provided as part of a computer LAN or WAN.

CROSS-REFERENCE AND PRIORITY CLAIMS TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/621,001, filed Jan. 8, 2007, and entitled “Associative DatabaseScanning and Information Retrieval”, which is a continuation applicationof U.S. application Ser. No. 10/722,691, filed on Nov. 24, 2003, andentitled “Associative Database Scanning and Information Retrieval”, nowU.S. Pat. No. 7,181,437, which is a continuation of U.S. applicationSer. No. 09/545,472, filed Apr. 7, 2000, entitled “Associative DatabaseScanning and Information Retrieval”, now U.S. Pat. No. 6,711,558, theentire disclosures of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Associative memory devices are known in the prior art. Generally, theseassociative memory devices comprise peripheral memories for computers,computer networks, and the like, which operate asynchronously to thecomputer, network, etc. and provide increased efficiency for specializedsearches. Additionally, it is also known in the prior art that thesememory devices can include certain limited decision-making logic as anaid to a main CPU in accessing the peripheral memory. An example of suchan associative memory device particularly adapted for use with arotating memory such as a high speed disk or drum can be found in U.S.Pat. No. 3,906,455, the disclosure of which is incorporated herein byreference. This particular device provides a scheme for use with arotating memory and teaches that two passes over a memory sector isnecessary to presort and then sort the memory prior to performing anylogical operations thereon. Thus, this device is taught as not beingsuitable for use with any linear or serial memory such as magnetic tapeor the like.

Other examples of prior art devices may also be found in U.S. Pat. Nos.3,729,712; 4,464,718; 5,050,075; 5,140,692; and 5,721,898; thedisclosures of which are incorporated herein by reference.

As an example, in U.S. Pat. No. 4,464,718, Dixon performs fixedcomparisons on a fixed number of bytes. They don't have the ability toscan and correlate arbitrarily over the data. They search serially alongthe tracks in a given disk cylinder but there is no provision forparallel searching across disks. Dixon's comparisons are limited by afixed rigid number of standard logical operation types. Additionally,the circuitry presented supports only these single logical operations.There is no support for approximate or fuzzy matching.

While these prior art associative memory devices represent an attempt tospeed the input and output of information to and from a peripheralmemory, which in many cases is a mass storage memory device, all rely onthe classic accessing of data stored in digital form by reading andinterpreting the digital either address or content of the memorylocation. In other words, most such devices access data by its addressbut there are some devices that take advantage of the power of contentaddressing as is well known in the art. Nevertheless, in all of theprior art known to the inventors, the digital value of the address ordata contained in the addressed location must be read and interpreted inits digital form in order to identify the data and then select it forprocessing. Not only does it take processing time to read and interpretthe digital data represented by the address or content, this necessarilyrequires that the accessing circuit process the memory according to thestructure of the data stored. In other words, if the data is stored inoctets, then the accessing circuitry must access the data in octets andprocess it in an incremental manner. This “start and stop” processingserves to increase the input/output time required to access data. As isalso well known in the art, this input/output time typically representsthe bottleneck and effective limitation of processing power in anycomputer or computer network.

In order to solve these and other problems in the prior art, theinventors herein have succeeded in designing and developing a method andapparatus for an associative memory in several embodiments which providean elegantly simple solution to these prior art limitations as well asdramatically decreased access times for data stored in mass storagememories. As mentioned, the invention has several embodiments each ofwhich has its own advantages.

Generally, the invention may be described as a technique for dataretrieval through approximate matching of a data key with a continuousreading of data as stored on a mass storage medium. In its broadest, andperhaps most powerful, embodiment, this key may be an analog signal andit is matched with an analog signal generated by a typical read/writedevice as it slews across the mass storage medium. In other words, thesteps taught to be required in the prior art of not only reading theanalog representation of digital data stored on the mass storage mediumbut also the conversion of that signal to its digital format prior tobeing compared are eliminated. Furthermore, there is no requirement thatthe data be “framed” or compared utilizing the structure or format inwhich the data has been organized and stored. For an analog signal, allthat need be specified is the elapsed time of that signal which is usedfor comparison with a corresponding and continuously changing selectedtime portion of the “read” signal. Using any one of many standardcorrelation techniques as known in the prior art, the data “key” maythen be approximately matched to the sliding “window” of data signal todetermine a match. Significantly, the same amount of data may be scannedmuch more quickly and data matching the search request may be determinedmuch more quickly as well. For example, the inventors have found thatCPU based approximate searches of 200 megabytes of DNA sequences cantake up to 10 seconds on a typical present day “high end” system,assuming the offline processing to index the database has already beencompleted. In that same 10 seconds, the inventors have found that a10-gigabyte disk could be magnetically searched for approximate matchesusing the present invention. This represents a 50:1 improvement inperformance. Furthermore, in a typical hard disk drive there are foursurfaces and corresponding read/write heads, which may be all searchedin parallel should each head be equipped with the present invention. Asthese searches can proceed in parallel, the total increase in speed orimprovement represents a 200:1 advantage. Furthermore, additional harddisk drives may be accessed in parallel and scaled to further increasethe advantage provided by the present invention.

By choosing an appropriate correlation or matching technique, and bysetting an appropriate threshold, the search may be conducted to exactlymatch the desired signal, or more importantly and perhaps morepowerfully, the threshold may be lowered to provide for approximatematching searches. This is generally considered a more powerful searchmode in that databases may be scanned to find “hits” which may be valideven though the data may be only approximately that which is beingsought. This allows searching to find data that has been corrupted,incorrectly entered data, data which only generally corresponds to acategory, as well as other kinds of data searches that are highlydesired in many applications. For example, a library of DNA sequencesmay be desired to be searched and hits found which represent anapproximate match to a desired sequence of residues. This ensures thatsequences which are close to the desired sequence are found and notdiscarded but for the difference in a forgivable number of residuemismatches. Still another application involves Internet searchesprovided by Internet search engines. In such a search, approximatematching allows for misspelled words, differently spelled words, andother variations to be accommodated without defeating a search orrequiring a combinatorial number of specialized searches. This techniquepermits a search engine to provide a greater number of hits for anygiven search and ensure that a greater number of relevant web pages arefound and cataloged in the search.

Still another possible application for the present invention is foraccessing databases which may be enormous in size or which may be storedas analog representations. For example, our society has seen theimplementation of sound recording devices and their use in many forumsincluding judicial proceedings. In recent history, tape recordings madein the President's oval office have risen in importance with respect toimpeachment hearings. As can be appreciated, tape recordings made overthe years of a presidency can accumulate into a huge database whichmight require a number of persons to actually listen to them in order tofind instances where particular words are spoken that might be ofinterest. Utilizing the present invention, an analog representation ofthat spoken word can be used as a key and sought to be matched while thedatabase is scanned in a continuous manner and at rapid speed. Thus, thepresent invention provides a powerful search tool for massive analogdatabases as well as massive digital databases.

While text-based searches are accommodated by the present invention asdescribed above, storage media containing pictures, sound, and otherrepresentations have traditionally been more difficult to search thantext. The present invention allows searching a large data space for thepresence of such content or fragments thereof. For example, the key inthis case could be a row or quadrant of pixels that represent the imagebeing sought. Approximate matching of the key's signal can then allowidentification of matches or near matches to the key.

While the principal advantages and features of the present inventionhave been briefly explained above, a more thorough understanding of theinvention may be attained by referring to the drawings and descriptionof the preferred embodiment which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a computer having access through its systemor input/output bus to the present invention comprising the logical massstorage medium for asynchronous access thereto, as well as a networkinterface between the present invention and a network to other computersystems;

FIG. 1A is a schematic for a conventional rigid disk drive systemillustrating different insertion points for connection of the presentinvention;

FIG. 2 is a block diagram depicting the implementation of the presentinvention in a stand-alone configuration;

FIG. 3 is a block diagram depicting the present invention implemented asa shared remote mass storage device across a network;

FIG. 4 is a block diagram depicting the present invention as a networkattached storage device (NASD);

FIG. 5 is a flow chart detailing the logical steps in the inventivemethod for accessing data in a mass storage medium;

FIG. 6 is a graphical representation of an analog signal as might beused as a key;

FIG. 7 is a graphical representation of an analog signal representingthe continuous reading of data from a mass storage medium in which the“key” data pattern is present;

FIG. 8 is a graphical representation of the key signal overlying andmatched to the data signal;

FIG. 9 is a graphical representation of a correlation functioncalculated continuously as the data in the mass storage medium isscanned and compared with the key; and

FIG. 10 is a graphical representation of a correlation function as thekey is continuously compared with a signal taken from reading adifferent set of data but which also contains the “key” data pattern.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, the present invention is readily implemented in astand-alone computer or computer system. In broad terms, the presentinvention is comprised of an approximate matching and pre-fetchprocessor 20 which itself comprises a programmable digital logic deviceor microprocessor 22 coupled to an approximate matching unit 24. A massstorage medium 26 is connected to the approximate matching unit 24 andprovides the medium for storing large amounts of data. The term “massstorage medium” should be understood as meaning any device used to storelarge amounts of data, and which is typically designated for use in acomputer or computer network. Examples include optical systems such asCD ROMS, magnetic systems such as hard disk drives or sub-units such asa single disk surface, and these systems may be rotating, linear,serial, parallel, or various combinations of each. For example, a rackof hard disk drive units could be connected in parallel and theirparallel output provided at the transducer level to one or moreapproximate matching units 24. Similarly, a bank of magnetic tape drivescould be used, and their serial outputs each provided in parallel to oneor more approximate matching units 24. The data stored on the medium maybe in analog or in digital form. For example, the data could be voicerecordings as in the tape recording example given above. The presentinvention is thus scalable, permitting an increase in the amount of datastored in a mass storage system (by increasing the number of parallelstorage units) while preserving the performance (by increasing thenumber of parallel approximate matching units or replicating theapproximate matching and prefetch processor).

In the prior art as shown in the upper portion of FIG. 1, typically adisk controller 28 and/or a disk cache 30 may be used in the traditionalsense for access by a CPU 32 over its system or input/output bus 34. Inthe present invention, the approximate matching and pre-fetch processor20 accesses data in the mass storage medium 26 and presents it for useat the system bus 34 without moving large blocks of memory from the massstorage medium 26 over the system bus 34 and into the main memory (notseparately shown) of CPU 32 for sorting and accessing. In other words,as is explained in greater detail below, the CPU 32 sends a data requestor query to the approximate matching and pre-fetch processor 20 whichthen asynchronously accesses and sorts data in the mass storage medium26 and presents it for use either in a disk cache 30 as is known in theprior art or directly onto the system bus 34 without further processingbeing required by CPU 32 or use of its main memory. The processor isthus free to perform other tasks while the searching and matchingactivity is being performed by the present invention.

The approximate matching unit 24 may itself comprise a set of digitallogic or analog circuitry organized to perform scanning, correlation,general logic and approximate matching functions on the signals receivedfrom the storage medium in conjunction with digital or analogrepresentations of query directed key information. The functions may beperformed by dedicated logic and circuitry, programmable logic andcircuitry or by use of programmable processors such as digital signalprocessors (DSPs). The inventors contemplate that many differentvariations of hardware or programmed software devices may be used tovirtually equal advantage in implementing the present invention andtherefore do not contemplate any particular implementation as a bettermode than another, at present, except as otherwise expressed herein.Furthermore, the present invention should not be considered as beingtied to any specific data structure or application, those having beenused herein are instead to be viewed as illustrative only. Using thepresent disclosure as a template, it is contemplated that one ofordinary skill in the art could readily construct a device as wouldperform the functions and operation necessary to achieve the purposes ofthe invention.

As has been explained above, the present invention may be used toperform both exact matches and approximate matches. When performing anexact match in the analog domain, at Point A in FIG. 1A, where matchingis done using analog comparators and correlation techniques, there anexact match corresponds to setting a sufficiently high threshold valuefor matching the key with analog source data on the storage medium.Approximate matching in this analog domain corresponds to settingappropriate (lesser) threshold values. When performing an exact match inthe digital domain, an exact match is performed using digitalcomparators and logic as suggested in current art, where a digital keyis compared with digital source data from the storage medium. Suchmatching could be performed at Point B or Point C, as shown in FIG. 1A,which corresponds to the pre- and post-error-corrected digital signal,respectively. Approximate matching in this domain corresponds toperforming comparisons or digital correlation of the digital key withdigital source data obtained from the storage medium. The digital keymay contain “wild card” or “don't care” digital bits or data formats.The success of an approximate match may be determined by setting acorrelation value or by using one of a number of matching-performancemetrics such as the number of bits within a key that are equal to thecorresponding bits in the scanned source data. Also, note that the dataentries identified in an “approximate” match search will include the“exact” hits that would result from an “exact” search. For clarity, whenthe word “match” is used, the reader should understand that it includesa search or a data result found through either of an approximate searchor an exact search. When the phrase “approximate match” or even just“approximate” is used, the reader should understand that it could beeither of the two searches described above as approximate searches, orfor that matter any other kind of “fuzzy” search that has a big enoughnet to gather data entries that are loosely related to the searchcriteria. Of course, an exact match is just that, and does not includeany result other than an exact match of the search criteria with a highdegree of correlation.

The microprocessor or programmable logic device 22 may itself compriseone or more microprocessors, programmable logic units, dedicated logicand associated circuitry. This unit interfaces with the system orinput/output bus 34 and, in one configuration, also interfaces with anydisk caches 30 which may be present. The unit receives and processesrequests and queries from the CPU 32 or network interface 36 andpresents these requests in the appropriate form to approximate matchingunit 24. Additionally the unit may aid in passing the results of therequests to either or both the disk cache 30 and/or the CPU 32 (by wayof the bus 34).

More particularly, as shown in FIG. 1A, a conventional rigid disk drivemay have a plurality of rotating disks with multiple transducersaccessing each disk. Each of these transducers typically has its outputfeeding analog signal electronics, such as amplifiers. This isrepresented at point A in the Figure. The Approximate Matching andPre-fetch Processor (AMPP) 20, or the AMU 24, may be installed at pointA for analog matching. As further shown in FIG. 1A, typically theoutputs of the analog circuitry are selectively provided to a singledigital decoder which then processes one such output. This isrepresented at point B in the Figure. This digital output is typicallythen sent through error correction circuitry (ECC) and at its output Cis then passed on to the bus 34 or disk cache 30. For purposes of thepresent invention, it may be desirable to provide multiple parallelpaths for data by providing multiple digital decoders and ECC's. TheApproximate Matching and Pre-fetch Processor (AMPP) 20, or the AMU 24,may be installed at either of points B or C for digital matching, andfor multiple data output, multiple AMPP's or AMU's may also be provided.

Also shown in FIG. 1 is a network interface 36 interconnecting thepresent invention 20, a network 38 which may be a LAN, WAN, Internet,etc. and to which other computer systems 40 may be connected. With thisarrangement, other computer systems 40 may conveniently also access thedata stored on the mass storage medium 26 through the present invention20. More specific examples are given below.

As shown in FIGS. 2-4, the present invention may be implemented in avariety of computer and network configurations. As shown in FIG. 2, thepresent invention may be provided as part of a stand-alone computersystem 42 comprising a CPU 44 connected to a system bus 46 which thenaccesses a mass storage medium 48 having the invention as disclosedherein.

As shown in FIG. 3, the mass storage medium 50 coupled with the presentinvention may be itself connected directly to a network 52 over which aplurality of independent computers or CPU's 54 may then access theintelligent mass storage medium 50. The intelligent mass storage medium50 may itself be comprised of a bank of hard disk drives comprising aRAID, disk farm, or some other massively parallel memory deviceconfiguration to provide access and approximate matching capabilities toenormous amounts of data at significantly reduced access times.

As shown in FIG. 4, an intelligent mass storage medium 56 equipped withthe present invention may be connected to a network 58 as a NetworkAttached Storage Device (NASD) such that over the network 58 a pluralityof stand-alone computers 60 may have access thereto. With theconfiguration as shown in FIG. 4, it is contemplated that each datastorage device, represented as a disk in FIG. 4, would be accessiblefrom any processor connected to the network. One such configurationwould include assigning a unique IP address or other network address toeach data storage medium.

The configurations as exemplified by those shown in FIGS. 2-4 representonly examples of the various computer and network configurations withwhich the present invention would be compatible and highly useful.Others would be apparent to those having skill in the art and thepresent invention is not intended to be limited through the examples asshown herein which are meant to be instead illustrative of theversatility of the present invention.

As shown in FIG. 5, the method of the present invention is describedalternatively with respect to whether an analog or digital key is used.However, beginning at the start of the method, a CPU performs certainfunctions during which it may choose to access data stored in a massstorage medium. Typically, the CPU runs an application 62 which may be aDNA search, an Internet search, an analog voice search, a fingerprintsearch, an image search, or some other such search during which anapproximate (or exact) match to data is desired. In executing thathigher order language application, the CPU would typically execute arequest or query to obtain information from the storage device 26. Thequery contains directives specifying various parameters which the diskcontrol unit 28 and the approximate matching and prefetch processor 20must have to properly obtain requested information from the storagedevice 26. Examples of parameters include but are not limited to thefollowing: the starting location for scanning the storage device; thefinal location after which (if there is not match) scanning isterminated; the key to be used in the scanning; a specification of theapproximate nature of the matching; what information should be returnedwhen a match occurs, etc. The sort of information that can be returnedincludes the address of the information where the match was found, or asector, record, portion of record or other data aggregate which containsthe matched information. The data aggregate may also be dynamicallyspecified in that the data returned on a match may be specified to bebetween bounding data specifiers with the matched data contained withinthe bounding field. For example, looking for the word “terrorist” in astring of text might find the approximate match, due to misspelling, ofthe word “terrerist”, and return a data field which is defined by thesurrounding sentence. Another query parameter would indicate whether thereturned information should be sent to the system or input/output bus34, or the disk cache 30.

The query will typically result in the execution of one or moreoperating system utilities. As an example of a higher level utilitycommand, for the UNIX operating system, this could be modified versionsof glimpse, find, grep, apropos. Other such functions causing the CPU tosend commands 66 such as search, approximate search, etc., to theapproximate matching and pre-fetch processor of the present invention(see FIG. 1) with relevant portions of these commands also being sent tothe disk controller 28 to, for example, initiate any mass storage mediapositioning activity 69 that is later required for properly readinginformation from the media.

At this point, depending upon the particular methodology desired to beimplemented in the particular embodiment of the invention, it would benecessary that an analog or digital key is determined. This key is data,exact or approximate, that corresponds to the data being searched for.For an analog key, this key may either be pre-stored such as in the massstorage medium, developed using dedicated circuitry, or required to begenerated. Should the analog key be pre-stored, a send pre-stored keystep 68 would be performed by the microprocessor or programmable logicdevice 22 (see FIG. 1) which would transmit the key in digital andsampled format to the approximate matching unit 24 as shown in step 70.Alternatively, should the analog key not be pre-stored, the analog keycan be developed using one of a number of mechanisms, two of which areshown in FIG. 5. In one the microprocessor 22 would write the key on themagnetic medium as at step 72 and then next read the key as at step 74in order to generate an analog signal representation of the key. Inanother as at step 71 the digital version of the key received from theCPU would be converted using appropriate digital to analog circuitry toan analog signal representation which would in turn be appropriatelysampled. The key would then next be stored as a digital sample thereofas in step 70. Should a digital key be used, it is only necessary thatthe microprocessor 22 store the digital key as at step 76 in approximatematching unit 24. It should be understood that depending upon theparticular structures desired to be included for each of themicroprocessor 22 and approximate matching unit 24, the key may residein either or all of these components, it merely being preferable toultimately get the appropriate digital format for the key into theapproximate matching unit 24 for comparison and correlation. Next, afterthe mass storage device reaches its starting location as at 79, the datastored on the mass storage medium 26 is continuously read as at step 78to generate a continuous stream signal representative of the data storedin the mass storage medium 26. Should an analog key have been used, thisanalog key may then be correlated with an analog read of data from themass storage medium 26 as at step 80. While the inventors contemplatethat any of many prior art comparators and correlation circuitry couldbe used, for present purposes the inventors suggest that a digitalsampling of the analog signal and key could be quite useful forperforming such comparison and calculating the correlation coefficient,as explained below. It is noted that this analog signal generated fromreading the data from mass storage medium 26 may be convenientlygenerated by devices in the prior art from the reading of either analogor digital data, it not being necessary that a digital key be used tomatch digital data as stored in mass storage medium 26. Alternatively, acorrelation step 82 may be performed by matching the digital key with astream of digital data as read from the mass storage medium 26. Notethat the key reflects the inclusion of approximate information. Thus,correlating this with information read from the storage medium enablesapproximate matching capabilities.

Decision logic 84 would next make an intelligent decision as to whethera portion of data approximately matches or does not approximately matchthe key. Should a match be found, then the data is processed as at step86 and the data requested by the query is sent to a disk cache 30,directly onto system bus 34, or otherwise be buffered or made availableto a CPU 32, network interface 36, or otherwise as shown in FIGS. 1-4. Alogical step 88 is suggested in FIG. 5 for returning to the continuousreading of data from the mass storage medium 26, indicating perhaps a“do” loop. However, it should be understood that this is a continuousprocess and that data is processed from the mass storage medium 26 as astream and not in individualized chunks, frames, bytes, or otherpredetermined portions of data. While this is not precluded, the presentinvention preferably allows a key to be in essence “slid” over acontinuously varying data read signal such that there is no hesitationin reading data from the mass storage medium 26. There is no requirementto synchronize reading to the start or end of any multi-bit datastructure, or any other intermediate steps required to be performed asthe data is compared continuously “on the fly” as it is read from themass storage medium 26. This type of comparison and correlation may bereferred to as a pattern match or comparison. Eventually, the dataaccess is completed as at step 90 and the process completed.

The inventors herein have preliminarily tested the present invention andhave generated preliminary data demonstrating its operability andeffectiveness.

FIG. 6 is a graphical representation of a measured analog signal outputfrom a read/write head as the read/write head reads a magnetic medium onwhich is stored a 10-bit digital key. As shown therein, there are peaksin an analog signal which, as known in the art, represents the trueanalog signal generated by a read/write head as data is read from amagnetic medium such as a hard disk. The scales shown in FIG. 6 arevolts along the vertical axis and tenths of microseconds along thehorizontal axis.

As shown in FIG. 7, an analog signal is generated, again by a read/writehead, as data is read from a pseudo-random binary sequence stored in atest portion of a magnetic medium. As can be seen in FIG. 7, the readsignal does not provide an ideal square wave output when examined atthis level.

FIG. 8 is a graphical representation, with the horizontal scaleexpanded, to more specifically illustrate the overlap betweenapproximately two bits of the 8-bit key and the corresponding two bitsfound in the pseudo-random binary sequence encoded at a differentlocation on the disk or magnetic medium.

FIG. 9 is a graphical representation of a correlation coefficientcalculated continuously as the comparison is made between the key andthe continuous reading of data from the hard disk. This correlationcoefficient is calculated by sampling the analog signals at a high rateand using prior art signal processing correlation techniques. One suchexample may be found in Spatial Noise Phenomena of Longitudinal MagneticRecording Media by Hoinville, Indeck and Muller, IEEE Transactions onMagnetics, Volume 28, no. 6, November 1992, the disclosure of which isincorporated herein by reference. A prior example of a reading,comparison, and coefficient calculation method and apparatus may befound in one or more of one of the co-inventor's prior patents such asU.S. Pat. No. 5,740,244, the disclosure of which is incorporated hereinby reference. The foregoing represent examples of devices and methodswhich may be used to implement the present invention, however, asmentioned elsewhere herein, other similar devices and methods may belikewise used and the purposes of the invention fulfilled.

At approximately the point labeled 325, a distinct peak is noted whichapproaches 1, indicating a very close match between the key and thepseudo-random binary sequence. Thus, the present invention has beendemonstrated as capable of finding a key that is present in apseudo-random digital sequence. FIG. 9 is also illustrative of theopportunity for approximate matching which is believed to be a powerfulaspect of the present invention. Looking closely at FIG. 9, it is notedthat there are other lesser peaks that appear in the correlationcoefficient. Thus, if a threshold of 0.4 were established as a decisionpoint, then not only the peak occurring which approaches 1 wouldindicate a match or “hit” but also another five peaks would beindicative of a “hit”. In this manner, a desired coefficient value maybe predetermined or adjusted as desired to suit particular searchparameters. For example, when searching for a particular word in a largebody of text, lower correlation values may indicate the word is presentbut misspelled.

FIG. 10 depicts the continuous calculation of a correlation coefficientbetween the same 8-bit key but with a different data set. Again, asingle match is picked up at approximately 200 microseconds. It is alsonoted that should a lower threshold be established additional hits wouldalso be located in the pseudo-random data.

Various changes and modifications to the present invention would beapparent to those skilled in the art but yet which would not depart fromthe spirit of the invention. Several of these alternatives have beenindicated above. For example, all of the operations exemplified by theanalog processing shown in FIGS. 6-10, have their equivalentcounterparts in the digital domain. Thus, approximate matching andcorrelation types of processing can be done on the standard digitalrepresentation of the analog bit patterns. This can also be achieved ina continuous fashion using tailored digital logic, microprocessors anddigital signal processors, or alternative combinations. It is thereforethe inventors' intention that the present invention be limited solely bythe scope of the claims appended hereto, and their legal equivalents.

1-37. (canceled)
 38. A data storage device comprising an approximate matching and pre-fetch processor connected to a storage medium.
 39. The data storage device of claim 38 wherein the approximate matching and pre-fetch processor includes an approximate matching unit connected to the storage medium and a logic device connected to the approximate matching unit.
 40. The data storage device of claim 39 wherein said logic device comprises a data processor.
 41. The data storage device of claim 40 wherein said logic device comprises a digital data processor.
 42. The data storage device of claim 41 wherein said digital data processor comprises a microprocessor programmed to accept search inquiries from another digital data processor, interpret said search inquiries and translate them for determining an associated key therewith, and transmit a search inquiry and the determined key to the approximate matching unit.
 43. The data storage device of claim 41 wherein said digital data processor comprises a programmable logic device programmed to accept search inquiries from another digital data processor, interpret said search inquiries and translate them for determining an associated key therewith, and transmit a search inquiry and the determined key to the approximate matching unit.
 44. The data storage device of claim 42 wherein the approximate matching unit comprises a comparator for comparing the determined key with data read from the storage medium and determining a match therebetween.
 45. The data storage device of claim 43 wherein the approximate matching unit comprises a comparator for comparing the determined key with data read from the storage medium and determining a match therebetween.
 46. The data storage device of claim 38 wherein the approximate matching and pre-fetch processor includes an approximate matching unit, the storage medium includes at least one storage surface, a digital decoder in circuit with an output of said surface, and the approximate matching unit is connected between said storage surface and the digital decoder.
 47. The data storage device of claim 38 wherein the approximate matching and pre-fetch processor includes an approximate matching unit, the storage medium includes at least one storage surface, a digital decoder in circuit with an output of said surface, and the approximate matching unit is connected to an output of the digital decoder.
 48. The data storage device of claim 38 wherein the approximate matching and pre-fetch processor includes an approximate matching unit, the storage medium includes at least one storage surface, a digital decoder in circuit with an output of said surface, an error correction circuit in circuit with the output of said digital decoder, and the approximate matching unit is connected to an output of the error correction circuit.
 49. A computer having a main processor, a working memory, a supplemental memory, and an approximate matching and pre-fetch processor, said pre-fetch processor being directly coupled to said supplemental memory and configured to match a determined key representative of data sought to be retrieved from said supplemental memory with a data signal representative of a continuous stream of data read from said supplemental memory.
 50. A network attached mass storage device (NASD), said NASD comprising a mass storage device coupled to an approximate matching and pre-fetch processor, said NASD having a network addressable input/output port for receiving data inquiries and responding thereto.
 51. A computer having a main processor, a working memory, a supplemental memory, and an approximate matching and pre-fetch processor, said pre-fetch processor being directly coupled to said supplemental memory and configured to approximately match a determined key representative of data sought to be retrieved from said supplemental memory with a data signal representative of a continuous stream of data read from said supplemental memory. 